The invention relates to a method of operating an internal combustion engine plant. The invention is particularly suitable for optimizing engine operation during the start-up period so as to achieve the lowest possible noxious emissions. The invention is also especially suitable for internal combustion engine plants which are part of a hybrid drive as it may be used for example in motor vehicles.
In conventional starting procedures, the internal combustion engine is driven to a predetermined low speed far under engine idling speed whereupon ignition and fuel injection are activated at the same time. The engine is driven for example by an electric starter motor utilizing the energy of an on-board battery of the vehicle or, in the case of a hybrid drive, by the energy stored in an energy storage device, such as a flywheel or a traction battery, during a previous operating cycle of the engine.
In order to reduce noxious emissions specifically during engine startups, the use of exhaust gas catalytic converters is known which are heated electrically or by additional fuel combustion in the exhaust gas system of the internal combustion engine, see for example patent publication DE 43 39 686 C1 and the magazine publication "Heated Catalytic Converter" in Automotive Engineering, September 1994, page 31. By being actively heated such exhaust gas catalytic converters reach the operating temperature required for the conversion of pollutants sooner, particularly for the oxidation of carbon monoxide and unburnt hydrocarbons. As a result, noxious emissions are reduced early during warm-up of the engine.
DE 195 32 325 C1 discloses an internal combustion engine of a series hybrid drive which is driven for start-up to a speed higher than its normal start-up speed. Preferably, at the same time, fuel is admitted to the engine already before the start up speed is reached and is ignited so that the engine speed is rapidly increased under full load conditions.
DOS 196 00 975 A1 discloses a control arrangement for a four cycle internal combustion engine wherein, during engine start-up, the fuel injection is not activated before the ignition is activated, but is activated immediately afterwards or preferably delayed by a fraction of the engine operating cycle or by a predetermined number of ignition cycles. In this way, back firing into the intake passages during start up of the engine is to be avoided.
It is the object of the present invention to provide a method of operating an internal combustion engine plant in such a way that a low noxious emission level can be achieved already during the engine start-up phase.